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The optimization module of OpenDSE

There is a newer version: 1.8

/**
 * OpenDSE is free software: you can redistribute it and/or modify it under the
 * terms of the GNU Lesser General Public License as published by the Free
 * Software Foundation, either version 3 of the License, or (at your option) any
 * later version.
 * 
 * OpenDSE is distributed in the hope that it will be useful, but WITHOUT ANY
 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
 * A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more
 * details.
 * 
 * You should have received a copy of the GNU Lesser General Public License
 * along with OpenDSE. If not, see http://www.gnu.org/licenses/.
 */
package net.sf.opendse.optimization.encoding.common;

import java.util.Collection;
import java.util.HashSet;
import java.util.Set;

import org.opt4j.satdecoding.Constraint;
import org.opt4j.satdecoding.ContradictionException;
import org.opt4j.satdecoding.DefaultSolver;
import org.opt4j.satdecoding.Literal;
import org.opt4j.satdecoding.Model;
import org.opt4j.satdecoding.Solver;
import org.opt4j.satdecoding.TimeoutException;
import org.opt4j.satdecoding.VarOrder;

/**
 * This class performs a binary search on a linear search problem, i.e., it
 * search if some variables have to be 0 or 1 to fulfill all constraints.
 * 
 */
public class BinaryReachability {

	protected final Solver solver = new DefaultSolver(); 
	
	public Set search(Set constraints, Set literals) {
		
		Collection candidates = new HashSet(literals);
		
		try {
			for (Constraint constraint : constraints) {
				solver.addConstraint(constraint);
			}

			while (candidates.size() > 0) {
				Constraint constraint = new Constraint(">=", 1);

				for (Literal literal : candidates) {
					constraint.add(literal);
				}
				solver.addConstraint(constraint);

				Model model = solve();
				

				if (model == null) {
					break;
				}

				Set remove = new HashSet();
				for (Literal candidate : candidates) {
					Object var = candidate.variable();
					boolean phase = candidate.phase();

					if (model.get(var) != null && model.get(var) == phase) {
						remove.add(candidate);
					}
				}
				candidates.removeAll(remove);
			}

		} catch (ContradictionException e) {

		}

		Set lits = new HashSet();
		for(Literal candidate: candidates){
			lits.add(candidate.negate());
		}

		return lits;
	}

	protected Model solve() {

		try {
			return solver.solve(new VarOrder());
		} catch (TimeoutException e) {
			System.err.println("Timeout in preprocessing: " + this.getClass());
		}

		return null;
	}

}